Perpendicular electric field drives Chern transitions and layer polarization changes in Hofstadter bands

• Published in: Nature communications 2022-12, Vol.13 (1), p.7781-7781, Article 7781
• Main Authors: Adak, Pratap Chandra, Sinha, Subhajit, Giri, Debasmita, Mukherjee, Dibya Kanti, Chandan, Sangani, L. D. Varma, Layek, Surat, Mukherjee, Ayshi, Watanabe, Kenji, Taniguchi, Takashi, Fertig, H. A., Kundu, Arijit, Deshmukh, Mandar M.
• Format: Article
• Language: English
• Subjects: 639/301/119/2794; 639/301/119/995; 639/301/357/918/1052; Bilayers; Electric fields; Energy spectra; Graphene; Humanities and Social Sciences; Low temperature; multidisciplinary; Physics; Polarization; Science; Science (multidisciplinary); Superlattices; Switching; Topology
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-022-35421-z

Moiré superlattices engineer band properties and enable observation of fractal energy spectra of Hofstadter butterfly. Recently, correlated-electron physics hosted by flat bands in small-angle moiré systems has been at the foreground. However, the implications of moiré band topology within the single-particle framework are little explored experimentally. An outstanding problem is understanding the effect of band topology on Hofstadter physics, which does not require electron correlations. Our work experimentally studies Chern state switching in the Hofstadter regime using twisted double bilayer graphene (TDBG), which offers electric field tunable topological bands, unlike twisted bilayer graphene. Here we show that the nontrivial topology reflects in the Hofstadter spectra, in particular, by displaying a cascade of Hofstadter gaps that switch their Chern numbers sequentially while varying the perpendicular electric field. Our experiments together with theoretical calculations suggest a crucial role of charge polarization changing concomitantly with topological transitions in this system. Layer polarization is likely to play an important role in the topological states in few-layer twisted systems. Moreover, our work establishes TDBG as a novel Hofstadter platform with nontrivial magnetoelectric coupling. Moiré superlattices offer a rich platform fort the study of correlated and topological phases. Here, by using low-temperature magneto-transport measurements, the authors demonstrate electric-field induced switching between Chern states in twisted double-layer graphene in the Hofstadter regime.